Is political polarization making racial tensions worse?

We take for granted the fact that America's racial divide overlaps with our political one.

In 2013, Gallup found that 89 percent of Republicans were non-Hispanic whites. (Hispanic ethnic identity can overlap with white racial identity, hence the distinction.) The density of whites in the Democratic Party was lower, at 60 percent; the portion of the party that was non-Hispanic black was about a fifth.

During the Clinton administration, white Americans were about four points more likely to say they were Republican than Democrat. In 2013, according to Gallup, the margin was nine points.

While the Democratic Party is more racially diverse, black Americans are not very politically diverse. Pew Research regularly surveys to figure out the partisan blend in the country, and in 2014 it determined that whites were more likely to identify as Republican than Democrat, 49 percent to 40 percent — a margin that mirrors Gallup. Blacks, on the other hand, were over seven times as likely to say that they're Democrats.

This is important. A Republican Party that's mostly white. A black population that's mostly Democratic.

Pew recently detailed how members of the two major political parties feel about each other. More than half of those in each party view the other party very unfavorably, and about 9 in 10 view the other party unfavorably to some extent.

More disconcertingly, more than 4 in 10 Republicans and Democrats view members of the opposite party as "a threat to the nation's well-being."

This is not an endpoint in the polarization of the United States, but it is a good ways down a path we've been walking for a while. Pew has measured the ideological position of members of each party over time, and by animating that, the recent ideological split between the parties becomes visible.

We know, too, that political critiques often overlap with racial ones, however indirectly. Republicans are the party of "old white men"; the rise of Donald Trump has regularly been attributed to concerns from the country's racial majority about the country's diversifying population.

Meanwhile, Democrats want free stuff, Mitt Romney argued in 2012 — with Jeb Bush narrowing that to black voters last summer. In Pew's survey, a majority of Republicans and 70 percent of Democrats referred to members of the other party as "closed-minded." Forty-six percent of Republicans referred to Democrats as "lazy," historically a racially loaded pejorative. (A fifth of Democrats said the same about Republicans.)

As our Aaron Blake wrote on Thursday, attitudes about the Black Lives Matter movement — the most obvious contemporary overlap of race and politics — split by both race and party.

Blacks are most supportive, then Democrats (who are black and white), then whites (who are Democrats and Republicans) and then Republicans.

Since 2013 — before the rise of BLM after the deaths of Michael Brown and Eric Garner at the hands of police — Gallup has found a sharp decline in the perception of race relations in the country.

Contrast that with the 2011-to-2014 transition in the polarization animation above.

Race and partisanship are so sufficiently intertwined at this point that it can be hard to determine the effect one has on the other. Are attitudes about Black Lives Matter split by party because they're split by race? Have liberal politics shaped the movement as much as racial ones?

Then again, race and partisanship have always been intertwined. The once solidly Democratic South is no longer solidly Democratic, for the same reason that blacks are solidly Democratic today. The Republican Party's birth was itself a function of ending the slave trade — the most horrible manifestation of racism in the country's history.

The unanswerable question is the extent to which political polarization causes a deterioration in racial harmony, or vice versa. After the events of Thursday night, it's worth trying to figure out at least how we can navigate a 2016 presidential campaign — an election in which both sides are motivated strongly by dislike of the other party's candidate — without seeing our cultural bonds erode even further.